I put a cat back on my '94 Silverado with good results. The sound was better and the power was noticeable. I replaced it w/ a single outlet exhaust, but I was still pleased.
Remember to have the exhausts exit out the sides since it looks like you will be towing a trailer (An 11 second 6 cylinder?!! Hot Dawg!)

You will like the power and sound from your new exhaust. The only thing i dont like about cat-back exhausts is they connect to yor cats, cats are bad. Might as well put sand in your oil or water in your gas tank. LOL.

You might experience a slight drop in low-end torque though with the duals. Don't ask me personally why, just it happened to me when I installed them and I've read in a few places here about people having the same problem. Put on an intake and had it custom tuned and that seemed solve some of the problem.

Finally got around to installing my Flowmaster American Thunder cat back on my 06 Sierra. Did it in my driveway. Would have been quick and easy had one of the cat flange bolts not snapped off. Anyway, the exhaust has the super 40 series muffler. Great sound when you get on it, but surprisingly little drone while cruising at highway speeds. Chrome tips can be side or rear exit. Overall, very pleased for just over $350 bucks.